Solve this if you can! - The best puzzle I came accross :)

This question was asked by an ethical hacking company which visited my college for campus recruitment! This question blowed everybody's brains. None were able to answer it. Finally, we were dumbstruck after listening to the answer!!!

The question goes as follows:

There are 5 pill (tablet) bottles. Each bottle has 10 pills. Each pill weighs exactly 10 grams. Due to some defect in manufacturing, the pills in one of the bottles were underweighed by 1 gram (i.e. each pill of that defected bottle, weighed only 9 grams).

Now, the task is to find which bottle has the defective pills, BY MEASURING THE WEIGHT ONLY ONCE.

Hi Vijay,This is easy to find. Mark the bottle as 1,2,3,4 and 5. First take 1 pill from the first bottle and 2 pill from the second bottle and so on. So from 5 bottle you have taken 15 pills overall. Now calculate the weight of this 15 pill. If it is 4.9g then the defective pills is from first bottle.